The invention relates to a method as recited in the preamble of claim 1. U.S. Pat. No. 4,559,625 to Berlekamp et al and U.S. Pat. No. 5,299,208 to Blaum et al disclose the decoding of interleaved and error protected information, where an error pattern found in a first word may give a clue to locate errors in another word of the same group of words. Errors pointed at are relatively closer or more contiguous than other symbols of the word that would generate the clue. The references use a standardized format and a fault model with multisymbol error bursts across various words. Occurrence of an error in a particular word may imply a strong probability for an error to occur in a symbol pointed at in a next word or words. The procedure will often raise the number of errors that may be corrected before the mechanism fails.
The present inventor has recognized a problem with this method: a clue will materialize relatively late in the process when the clue originating information will have been demodulated as well as been fully corrected. This will complicate the use of higher level measures such as a retry read of the data during a later disc revolution. Also, the present inventor has recognized that part or all of the clues could be acquired against a lower investment in terms of the amount of redundancy.
In consequence, amongst other things, it is an object of the present invention to provide a coding format with less overhead that would allow earlier generating of at least part of the clues. Now therefore, according to one of its aspects the invention is characterized according to the characterizing part of claim 1.
The invention also relates to a method for decoding such information, a device for encoding and/or decoding such information, and a carrier provided with such information. Further advantageous aspects of the invention are recited in dependent Claims.